Overhaul Basic Memory docs

[nellins]

Summary

• Rework the docs into a Cloud-first, task-oriented structure while preserving Open Source guidance
• Add/refresh Cloud CLI, support, teams, shared notes, integrations, agent skills, schemas, AI-friendly docs, and maintenance checks
• Remove stale/duplicative pages and old screenshots; add reviewed screenshot manifest and docs audit notes

Review notes

• Best reviewed as a site preview, not only as a diff
• Local checks pass with zero docs warnings

Test plan

• npm run check:docs
• npm run build